Optical Limiting Study of Double Wall Carbon Nanotube-Fullerene Hybrids

21 Pages·2010·0.75 MB·English

Accepted Manuscript
Optical Limiting Study of Double Wall Carbon Nanotube-Fullerene Hybrids
Kang-Shyang Liao, Jun Wang, Daniel Früchtl, Nigel J. Alley, Enrico Andreoli,
Eoghan P. Dillon, Andrew R. Barron, Hansoo Kim, Hugh J. Byrne, Werner J.
Blau, Seamus A. Curran
PII: S0009-2614(10)00375-1
DOI: 10.1016/j.cplett.2010.03.010
Reference: CPLETT 28073
To appear in: Chemical Physics Letters
Received Date: 5 January 2010
Accepted Date: 2 March 2010
Please cite this article as: K-S. Liao, J. Wang, D. Früchtl, N.J. Alley, E. Andreoli, E.P. Dillon, A.R. Barron, H. Kim,
H.J. Byrne, W.J. Blau, S.A. Curran, Optical Limiting Study of Double Wall Carbon Nanotube-Fullerene Hybrids,
Chemical Physics Letters (2010), doi: 10.1016/j.cplett.2010.03.010
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ACCEPTED MANUSCRIPT
Optical Limiting Study of Double Wall Carbon
Nanotube-Fullerene Hybrids
Kang-Shyang Liao,a,* Jun Wang,b Daniel Früchtl,b Nigel J. Alley,a,c Enrico Andreoli,a Eoghan P.
Dillon,d Andrew R. Barron,d Hansoo Kim,e Hugh J. Byrne,f Werner J. Blaub,g and Seamus A. Currana
aInstitute for NanoEnergy, Department of Physics, University of Houston, Houston, Texas 77204, USA
bSchool of Physics and the Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College
Dublin, Dublin 2, Ireland
cSchool of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland.
dRichard E. Smalley Institute for Nanoscale Science and Technology, Center for Biological and Environmental
Nanotechnology, Carbon Nanotube Laboratory, Rice University, Houston, Texas 77005, USA
eMicroscopy and Imaging Center, Texas A&M University, College Station, TX 77843, USA
fFocas Institute, Dublin Institute of Technology, Dublin 8, Ireland
gSchool of Physics, Dublin Institute of Technology, Kevin Street, Dublin 2, Ireland

Corresponding Author:

Kang-Shyang Liao
[email protected]
Institute for NanoEnergy, Department of Physics, 617 Science & Research Building 1, University of Houston,
Houston 77004, USA
Tel: [phone]; Fax: [phone]
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Graphical Abstract
The double wall carbon nanotube-Fullerene hybrids exhibit superior optical limiting performance to
those of Fullerenes and CNTs.

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Abstract
In order to merge complementary temporal and spatial nonlinear optical characteristics of Fullerene and
carbon nanotubes, synthesis of double wall carbon nanotube-Fullerene hybrid was performed by
covalently linking DWNT and C by amination reaction with polyethylenimine. DWNT-Fullerene
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hybrids were characterized by thermogravimetric analysis, UV-vis spectroscopy and transmission
electron microscopy. Optical limiting performance of DWNT-Fullerene hybrids is superior to those of
Fullerenes and SWNTs at the same level (~ 80%) of transmission. Whereas nonlinear scattering is an
evident mechanism, reverse saturable absorption from Fullerene moieties has significant contribution.
Charge transfer between the DWNT and Fullerene moieties may play an important role of optical
limiting.
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1. Introduction
Recently, there has been increasing interest in the application of nanotechnology to protective
coatings, including polymer nanotubular thin film composites. The use of carbon nanotubes in
nanocomposites revealed a multiplicity of applications as nano-fillers in polymer hosts including
thermal sensors [1] and antistatic coatings [2]. However, the success of nanocomposite fabrication is
still dependent on developing reliable synthetic methods in forming their primary building blocks, a
process that is challenging at the nanoscale for both inorganic and organic nanomaterials. Nonetheless,
there have been significant advances in the use of nanocomposites in various optical applications,
including organic light emitting diodes [3] and optical limiters [4]. Since the invention of lasers in the
1960s, not only have they become powerful instruments for material assessment, but are also commonly
used in our daily life, such as surgery and telecom applications. Protection from lasers is consequently
not a trivial matter but is one of genuine concern from a public safety and technological perspective.
The development of optical limiting materials/devices provides a valuable solution to the dangers of
lasers, as well as various other forms of optical instruments being used. A successful optical limiter
should strongly attenuate intense, potentially dangerous laser beams, while exhibiting high
transmittance for low intensity ambient light. Investigating optical limiting materials/mechanisms/
devices is therefore a very important area of research [5-8]. In the forefront of this field is a quest for
ideal materials that include carbon nanomaterials [7,8], phthalocyanines [9,10], porphyrins [11],
organometallics, inorganic semiconductors and liquid crystals [5,6]. In particular, the carbon
nanomaterials: carbon black [12], fullerenes [13,14], carbon nanotubes (CNTs) [4,15-17] and graphenes
[18] all make a great contribution to laser protection applications.
During the past two decades, researchers have established several effective nonlinear optical (NLO)
mechanisms for optical limiting, namely, reverse saturable absorption (RSA), two-photon absorption
(TPA), free-carrier absorption, nonlinear scattering and nonlinear refraction [5,8]. Fullerene-C is
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considered an ideal optical limiter across the visible spectrum (from 400 to 700 nm) since it was first
studied by Tutt and Kost [14]. The primary mechanism of optical limiting for C is RSA, which
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involves formations of excited states (triplet-triplet) with an absorption cross section much larger than
that of the ground state, leading to nonlinear absorption. More recent studies show CNTs have potential
as a broadband optical limiter from 430 to 1064 nm [4,7,8,15]. Thermally-induced nonlinear scattering
and nonlinear refraction are found to be the dominant mechanisms. At low fluences, nonlinear scattering
comes from solvent microbubbles generated by heat transfer from CNTs. At high fluences, the
scattering is mainly due to formations of carbon microplasmas. Therefore, the superior optical limiting
performance of CNTs can be attributed to their unique electronic structures that absorb broadband
energy, as well as their large surface area that can effectively dispatch the energy to surrounding
environments. In contrast to Fullerenes with a quick response time in the picosecond regime, CNTs
generally respond at best in the nanosecond regime.
The development of nonlinear absorber–CNT hybrids by covalent or noncovalent combination has
been reported by several groups [19-23]. In this work, we report the synthesis, characterization and
optical limiting property of a covalent linked CNT-Fullerene hybrid. The hybrid is expected to merge
complementary temporal and spatial NLO characteristics of Fullerene and carbon nanotubes, resulting
in a viable optical limiting material satisfying most of requirements for laser protection.
2. Experimental Methods
Materials. DWNTs prepared using a CVD method (> 95% purity, O.D. of 4 nm and length of 5-20
µm) were obtained from Nanolab. Transmission electron microscope (TEM) images revealed that the
pristine DWNT sample is actually a mixture of SWNT, DWNT, TWNT and FWNT. Polyethylenimine
(PEI, branched, M = 10,000 Da), N,N-dimethylformamide (DMF, anhydrous, 99.8%), Fullerene-C
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(98%), chlorobenzene (anhydrous, 99.8%) were obtained from Aldrich and used as received.
Direct Amination of DWNTs. DWNTs (3 g) and polyethylenimine (M ~ 10,000) (15 g) were mixed in
n
250 mL of DMF. Sonication for 20 min and stirring at 50 ºC for 5 d formed the product, DWNT-PEI
10,000. The resulting suspension was filtered through a 0.20 µm nylon membrane and the precipitate
was washed with 1M HCl, 1M NaOH, water and methanol to remove any excess PEI. After drying, 5.5
g of the product was obtained. Characterization of the product was carried out by titration. A known
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amount of DWNT-PEI10,000 was added to 20 mL of 0.01M HCl. After sonicating the mixture for 1 h
at 25 C, an aliquot (5 mL) of the resulting HCl solution was titrated to a pH 9.0 endpoint using 0.01M
NaOH. The difference between the original amount of HCl and the amount of HCl titrated corresponded
to the loading of titratable amino groups on DWNT-PEI10,000 and was 0.9 mequiv of titratable amine
groups/g.
Synthesis of DWNT-PEI10,000-C . DWNT-PEI10,000 (300 mg), Fullerene-C (150 mg) and
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triethylamine (0.5 mL) were mixed in 20 mL of chlorobenzene. Sonication for 1 min and stirring at 100
ºC for 5 d formed the product, DWNT-PEI10,000-C . The resulting suspension was filtered through a
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0.20 µm nylon membrane and the precipitate was washed with chlorobenzene and methanol to remove
any excess C and triethylamine. After drying, 408 mg of the product was obtained.
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Synthesis of PEI10,000-C . PEI10,000 (50 mg), Fullerene-C (100 mg) and triethylamine (1.0 mL)
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were mixed in 10 mL of chlorobenzene. Sonication for 1 min and stirring at 100 ºC for 5 d formed the
product, PEI10,000-C . The resulting suspension was filtered through a 0.20 µm nylon membrane and
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the precipitate was washed with chlorobenzene and methanol until the filtrate became colorless. After
drying, 122 mg of the product was obtained.
Characterization. Thermogravimetric analysis (TGA) was recorded by SEIKO 1 TG/DTA 200 under
Ar or air from 30 to 950 oC. UV-vis spectra were recorded by an Ocean Optics HR2000+ high
resolution spectrometer using a Mikropack PH-2000-BAL Deuterium-Halogen light source. High
resolution micrographs were taken by an FEI TECNAI G2 20F transmission electron microscope. It was
operated at a 200 kV accelerating voltage, equipped with a ZrO /W Schottky field emission gun and a
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Gatan imaging filter slow-scan CCD camera (GIF Tridiem with 2k x 2k pixels). Bright field TEM
images were collected by the CCD camera of the TECNAI 20F.
Z-scan Measurement. NLO and optical limiting properties of DWNT-Fullerene hybrids were studied
using open aperture Z-scan method, which is widely adopted to investigate third-order NLO processes,
including nonlinear absorption, scattering and refraction. In this work, a Z-scan was performed using 6
ns pulses from a Q-switched Nd:YAG laser. After spatially removing higher-order modes, a laser beam
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was tightly focused with a 9 cm focal length lens. The laser was operated at its second harmonic, 532
nm, with a repetition rate of 10 Hz. Simultaneously, a focusing lens setup was arranged at ~30° to the
direct incident beam to monitor the scattered light from the dispersions. All samples were tested in 1.0
cm quartz cells.
3. Results and Discussion
Syntheses and studies of CNT-fullerene hybrids have been reported [24,25]. D’Souza et al. performed
syntheses of SWNT/Pyr-NH +/crown-C hybrids by supramolecular assembly and studied their
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photoinduced electron transfer [24]. The results suggested a possibility of electron transfer from SWNTs
to singlet excited Fullerenes in the hybrids. Wu et al. performed syntheses of grapevine SWNT-C
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hybrids by covalent amide formation between oxidized SWNT and C derivative [25].
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Characterizations revealed a ground-state electron-transfer trend from SWNT to C moieties in the
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grapevine nanostructure. Although these CNT-fullerene hybrids show great potential as materials for
nonlinear optics, their syntheses are prohibitively complicated and time consuming. Here, we
synthesized CNT-Fullerene hybrids using all commercial available reagents in only two steps. DWNTs
are first treated with an excess amount of polyethylenimine (PEI) in N,N-dimethylformamide (DMF) at
50oC to give DWNT-PEI10,000 by following a procedure described by Liao et al [26]. Similar
procedures were carried out by Dillon et al. for SWNT amination as well [27]. The PEI functionalized
DWNTs can readily disperse in common organic solvents and the free amines on PEI functionalized
DWNTs can act as nucleophiles. In the next step, DWNT-PEI10,000 was reacted with an excess amount
of C in chlorobenzene at 100 oC for 5 days, as shown in Figure 1. Amination of Fullerenes was first
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studied by Hirsch et al [28] and it is suggested that amination of CNTs involves a similar mechanism as
amination of Fullerenes [29].
Characterization of CNT-Fullerene hybrids included a series of chemical and physical analyses.
Thermogravimetric analysis (TGA) under Ar showed distinct differences between the PEI derivative of
DWNTs and starting DWNTs. As shown in Figure 2, as-received DWNTs exhibited a gradual weight
loss of 10% over a temperature range 30-950 C. DWNT-PEI10,000 exhibited a ~ 30% weight loss in
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the 250-350 ºC temperature range. The weight loss in this region was ascribed to loss of the grafted PEI
on DWNT samples. The TGA of DWNT-PEI10,000-C under Ar exhibited a ~ 25% weight loss at the
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same temperature range, this represented the loss of grafted PEI. However, no extra weight loss was
observed at higher temperature range. Presumably, both DWNT and C residue didn’t burn under Ar.
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This hypothesis was proved by a separate TGA of PEI10,000-C under Ar over a temperature range 30-
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800 C (data not shown). The TGA showed more than 60% of residue was left which can be ascribed to
the C residue. In order to differentiate the composition of remaining residue of DWNT-PEI10,000-C ,
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the next TGA was first carried out under Ar from 30 to 500 oC to fully degrade PEI, air was then
introduced to the heating chamber and the temperature was increased gradually to 650 oC. A sudden
drop of ~ 25% weight was observed at 520 oC, followed by a more gradual weight loss of another 45%
from 520 to 600 oC. The first sudden drop was ascribed to the loss of C because all C molecules
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should burn at the same temperature. While the gradual weight loss from 520 to 600 oC can be ascribed
to the loss of DWNT because it is dependent on the diameter and length of DWNTs. Each individual
DWNT should burn gradually under different temperature ranges.
The formation of DWNT-Fullerene hybrids was also confirmed by UV-vis spectroscopy. As shown in
Figure 3, relative to the spectrum of C , the spectrum of DWNT-PEI10,000-C in chlorobenzene
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showed a maximum absorption of 330 nm. The peak at 330 nm can be assigned to the allowed
1T →1A transition of C [30]. Direct evidence of the formation of nanotube-fullerene hybrids can be
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seen through high resolution TEM micrographs as well. As shown in Figure 4, while the image of a
pristine nanotube (left) shows a smooth surface covered with some amorphous carbon materials, a
monomeric form of C spheres (right) can be clearly seen to be attached to the inner and outer surfaces
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of the SWNT in the image of the nanotube-fullerene hybrid.
For the optical limiting study, the hybrid was dispersed in chlorobenzene and poly(m-
phenylenevinylene-co-2,5-dioctoxyp-phenylenevinylene) (PmPV), respectively. PmPV is a well-known
conjugated polymer used to disperse carbon nanotubes, resulting in property modified nanocomposites
[3,31]. The normalized transmission and scattered light as functions of incident energy density was
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shown in Figure 5. As the incident energy density was increased, intense scattered light was observed
from DWNT-Fullerene dispersions along with decreasing transmission. Therefore the nonlinear
scattering, arising from DWNT moieties, is regarded as one of the main mechanisms for optical
limiting. The mechanism leading to optical limiting effects in carbon nanotubes has been studied
intensively. The induced scattering centers are composed of solvent bubbles and carbon microplasmas.
Due to the solvent effect [8,17], the hybrid dispersed in chlorobenzene possess superior optical limiting
response and stronger scattered signal in comparison to the polymer dispersions. In addition, it is
believable that RSA from Fullerene moieties has significant contribution as well. The superior optical
limiting effect of the hybrids results from an accumulation of different mechanisms.
In order to evaluate the optical limiting ability of DWNT-Fullerene dispersions, we compare the
optical limiting response of this hybrid with that of Fullerenes and SWNTs. As shown in Figure 6, the
optical limiting performance of this hybrid is superior to those of Fullerenes and CNTs at the same level
of transmission. Table 1 summarizes the linear and NLO coefficients for these three materials.
4. Conclusion
In summary, synthesis and characterization of DWNT-Fullerene hybrids was performed to merge
complementary temporal and spatial NLO characteristics of Fullerene and carbon nanotubes. The
optical limiting performance of DWNT-Fullerene hybrids is superior to those of Fullerenes and SWNTs
at the same level of transmission. Future studies regarding mechanisms that contribute to this better
optical limiting performance and the influence of covalent linkages between DWNTs and C to optical
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limiting are currently underway.

Acknowledgement
The work is supported by the US Department of Energy under Grant No. DE-FG36-08GO88008 and in
part by the Science Foundation Ireland (SFI) under Grant No. 08/CE/I1432. J.W. thanks SFI for his
postdoctoral research fellowship.

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